This invention relates to the field of expandable intraluminal support devices and more particularly to stents covered with heterologous tissue.
Typically, stents are expandable, tubular metallic devices that are positioned within a patient""s vasculature or other body lumen and expanded in order to support a vessel or body lumen and allow the flow of blood or other body fluids. Often, the stents are formed from a deformable metal and delivered using a balloon-type catheter. By advancing the catheter through the body lumen, the stent may be delivered to a desired position. Inflating the balloon then deforms the stent into an expanded configuration, seating it within the artery or other body lumen. Other implementations make use of a self-expanding stent formed from a psuedoelastic material that is delivered in a constricted condition and when released spontaneously expands to an enlarged configuration. In other embodiments, a stent made of shape memory alloy (NiTi) is inserted into the body lumen in a martensitic phase and transforms to austenite which has an expanded memory when raised to a temperature above the transformation temperature, usually less than 45xc2x0 C.
Stents are often used in conjunction with an intravascular treatment for obstructive coronary artery disease, for example, ablation, atherectomy, and balloon procedures. The prior art has employed a number of mechanical and pharmacological strategies to reduce the restenosis rate, but none have been particularly effective. Accordingly, stents have been proposed to maintain the patency of a treated vessel and prevent restenosis. Using stents, restenosis rates have fallen to less than 20%.
Restenosis is thought to be a natural healing reaction provoked by injury from the intravascular procedure. The healing process frequently causes thrombosis and may lead to intimal hyperplasia that occludes the vessel. Although helpful in reducing restenosis, stents do not represent a complete solution. The framework of the stent may still allow migration and proliferation of the smooth muscle cells, while the stent itself can be thrombogenic. To address these problems, stents have been covered with DACRON, PTFE and autologous vein and the surface has been seeded with endothelial cells or otherwise treated. Each of these solutions suffer from certain drawbacks, such as not being biocompatible, lacking sufficient mechanical strength, having a surface that is difficult to prepare, lack of ready availability and being thrombogenic.
Thus, there remains a need for a stent capable of minimizing restenosis while having a consistency similar to the native artery, a non-thrombogenic surface and sufficient mechanical strength as well as being biocompatible and readily available. This invention satisfies these and other needs.
The invention is a stent assembly suitable for maintaining the patency of a bodily lumen, generally comprising an expandable, tubular framework comprising a stent at least in part within a cylinder of biocompatible, non-thrombogenic expandable material such as heterologous tissue. Preferably, the heterologous tissue comprises bovine pericardium, but other preferred embodiments include porcine pericardium, aortic leaflet and other suitable heterologous tissue. The expandable, tubular framework may be a conventional metallic stent.
This invention is also directed to a method for maintaining the patency of a bodily lumen comprising the steps of mounting a stent assembly of a tubular expandable, metallic framework forming the stent coaxially disposed within a cylinder of biocompatible, non-thrombogenic expandable material such as heterologous tissue on an expandable member on the distal extremity of a catheter; advancing the catheter through the bodily lumen until the stent assembly is positioned at a desired location; expanding the stent assembly by expanding the expandable member onto which the stent assembly is mounted to anchor it within the bodily lumen; contracting the expandable member, e.g. deflating the balloon, and withdrawing the catheter. The expanded cylinder of biocompatible, non-thrombogenic expandable material such as heterologous tissue should extend over a substantial portion, preferably all, of the stenotic region in which it is disposed.